U.S. patent number 5,228,186 [Application Number 07/921,636] was granted by the patent office on 1993-07-20 for method of manufacturing electro-fusion fittings.
This patent grant is currently assigned to Fusion Plastics Ltd.. Invention is credited to David Brettell, Robin B. Carter, David M. A. Kenworthy, Russell J. Kirk.
United States Patent |
5,228,186 |
Brettell , et al. |
July 20, 1993 |
Method of manufacturing electro-fusion fittings
Abstract
An electro-fusion pipe coupler includes an outer shell and an
electric resistance heating coil secured therein by an intervening
layer of injection moulded thermoplastic material. The coupler is
made by winding the wire onto a core which consists of two
separable parts inserting the core into the tubular shell,
attaching contacts to the wire ends and inserting them into holes
provided in the shell, and injecting molten material into the space
defined between the core and the shell to form the layer. For
injecting the material the core parts define therebetween radial
runners connected to a central sprue inlet and opening at
respective outlets spaced around the core.
Inventors: |
Brettell; David (South
Normanton, GB2), Kirk; Russell J. (Sutton in
Ashfield, GB2), Carter; Robin B. (Sheffield,
GB2), Kenworthy; David M. A. (Sheffield,
GB2) |
Assignee: |
Fusion Plastics Ltd.
(Chesterfield, GB2)
|
Family
ID: |
27264457 |
Appl.
No.: |
07/921,636 |
Filed: |
July 30, 1992 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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517725 |
May 2, 1990 |
5163713 |
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Foreign Application Priority Data
Current U.S.
Class: |
29/611;
156/274.2; 264/262; 264/272.18; 29/530; 29/619 |
Current CPC
Class: |
B29C
45/14467 (20130101); B29C 65/342 (20130101); B29C
65/3468 (20130101); B29D 23/005 (20130101); F16L
47/03 (20130101); B29C 65/348 (20130101); B29C
66/52292 (20130101); B29C 66/8161 (20130101); B29C
66/5221 (20130101); B29C 66/83413 (20130101); Y10T
29/49098 (20150115); Y10T 29/49993 (20150115); Y10T
29/49083 (20150115) |
Current International
Class: |
B29C
45/14 (20060101); B29D 23/00 (20060101); F16L
47/02 (20060101); F16L 47/03 (20060101); H05B
003/00 () |
Field of
Search: |
;29/611,619,527.1,530
;264/262,272.18,279.1 ;285/21 ;219/535,544 ;156/274.2,294 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Echols; P. W.
Attorney, Agent or Firm: Watson, Cole, Grindle &
Watson
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a divisional of application Ser. No. 517,725,
filed May 2, 1990 now U.S. Pat. No. 5,163,713.
Claims
We claim:
1. A method of manufacturing an electro-fusion pipe coupler,
comprising the steps of preparing a shell with a cylindrical wall,
winding a coil of electrical resistance heating wire coated with
thermoplastics material onto a mould core, inserting the core and
the winding thereon into the shell with a radial space being
defined therebetween, injecting thermoplastic material between the
core and the shell wall to fill said space, and removing the core
so that the winding is retained in the shell by the moulded
material.
2. A method as claimed in claim 1, wherein preparing the shell
includes machining the inside surface thereof to form a
circumferential groove in the inner surface of the shell wall at
each end of the shell.
3. A method as claimed in claim 1, wherein the shell is prepared
from thermoplastic material, and the preparation of the shell
includes machining the inside surface of the shell wall thereof to
a relatively rough surface finish.
4. A method as claimed in claim 1, wherein the shell is prepared
from a tubular blank cut off from an extruded plastics pipe.
5. A method as claimed in claim 1, wherein the shell is prepared
from a tubular blank formed by winding an extruded ribbon of
thermoplastics material onto a drum.
6. A method as claimed in claim 1, wherein the preparation of the
shell includes producing at least one hole through the shell wall
for receiving a contact assembly.
7. A method as claimed in claim 6, wherein a contact part is
attached to an end of the wire and introduced into the radial hole,
and the thermoplastics material is injected to cover the contact
part on the interior of the shell.
8. A method as claimed in claim 7, wherein said contact part is
temporarily held in position by a fixing device engaged with the
contact part from outside the shell during the injection moulding
step.
9. A method as claimed in claim 1, wherein the wire is wound in two
tightly wound sections with a link portion connecting said
sections, the adjacent turns being in contact with each other.
10. A method as claimed in claim 1, wherein the thermoplastics
material is injected through the core.
Description
This invention relates to electro-fusion fittings and their
manufacture. Electro-fusion fittings are used for making couplings
in thermoplastics, most commonly polyethylene pipe. The invention
is particularly concerned with fittings intended for connecting two
pipe lengths end-to-end, such fittings being frequently referred to
as welding muffs or sleeves. Conventional welding sleeves consist
of a hollow cylindrical body of thermoplastic material with a coil
of electrical resistance heating wire at its inner surface. In use,
the pipe ends are pushed into the opposite ends of the sleeve and
an electric current is supplied to the heating coil so that the
material of the pipes and fitting body is melted and fuses together
to form a secure, leakproof coupling between the pipe ends.
Different methods can be employed for manufacturing electro-fusion
sleeves. Most convenient in the case of sleeves of relatively small
diameter, and hence having bodies of relatively small mass, is a
technique wherein the body is produced by a normal injection
moulding process. The heating wire, coated in the thermoplastic
material, may be wound onto an injection mould core and then have
the body injection moulded in situ over the wire coil.
This technique is not ideal for manufacturing large diameter
fittings, however, because tooling costs are very high and the
production rate is very low due to a long cycle time (in the order
of 20 minutes) which arises through the time it takes to fill the
mould cavity with molten plastic and the subsequent curing time
necessary before the mould can be opened. As a solution to the
problem of producing economically large diameter fittings, it has
been proposed in GB-A-2036518 to form the body by cutting a length
off from a pipe of thermoplastic material. The heating coil is
applied to the interior of the pipe length by a process which
involves: expanding the pipe length and introducing into it a
mandrel onto which the wire, either bare or coated with
thermoplastic material, has been wound; the pipe length is shrunk
onto the mandrel and winding in a furnace; electric current is
supplied to the heating wire to cause the wire turns to expand
while the mandrel is expanded or shrinking of the pipe length is
continued, and the thermoplastic material is caused to flow between
the turns; and, after cooling the wire ends are connected to
contact pins previously mounted on the pipe length. Thus, the
procedure is complicated and there still exists a need for a
reliable and economic manufacturing method.
SUMMARY OF THE INVENTION
In accordance with one aspect the present invention provides an
electro-fusion pipe coupler comprising an outer shell in the form
of a self-supporting cylinder, an electrical resistance heating
winding comprising a coil of wire coated with thermoplastic
material housed within the shell, and a layer of thermoplastic
material moulded in situ between the winding and shell and securing
the winding within the shell.
In such a construction, the main purpose of the outer shell is to
impart the necessary strength to the fitting. While it is preferred
that the shell is made from thermoplastic material, it may be
possible for it to be made from other materials such as metal. This
possibility exists because it may not be necessary for the shell to
partake in the pipe welding process as the moulded thermoplastic
layer, in combination with the wire coating material, may be
adequate to ensure a leakproof joint between two pipe ends.
During the injection moulding step the shell constitutes an outer
mould part confining the mould cavity with a core onto which the
wire is wound. Consequently expensive moulding apparatus can be
obviated. Even if the shell is made of thermoplastic material, an
integral bond uniting the shell and injection moulded layer will
not necessarily be obtained by the injection moulding process,
although the two parts will be in direct face-to-face contact. In
order to prevent the moulded layer breaking away or delaminating
from the inner surface of the shell due to the shrinkage which
tends to occur naturally during curing of the moulded material, it
is preferable for the moulded layer to be formed at each end with
an external projection in abutment with an axially outwardly facing
shoulder defined by the shell. The shoulder could be defined by the
end face of the shell, or by a rebate at the inner edge of the end
face. Also, the shoulder could be inclined to the axis, or formed
in some other way to provide a secure interlock with the moulded
layer. However, very satisfactory results have been obtained with a
radial shoulder defined by an annular groove machined in the inner
surface of the shell at a small distance in from the end.
It is preferable for the moulded layer to extend axially from end
to end of the shell. If the shell is made of thermoplastic
material, however, two discrete layers could be possible, these
layers being associated with winding portions arranged for
cooperation with respective pipe ends during the welding
procedure.
At each end of the coupler the lining formed within the shell by
the moulded layer can conveniently be chamfered to provide a
lead-in for the ends of the pipes to be coupled together.
A further advantage of the invention is that by limiting the amount
of injected material, dimensional accuracy of the finished bore is
more easily achieved.
According to another preferred feature, the coupler comprises a
contact pin assembly extending through the wall of the shell and
comprising an inner part held in place by the moulded layer, and an
outer part connected to the inner part and providing a terminal
portion. The inner and outer parts are joined releasably, e.g. by a
threaded connection. This contact construction has certain
advantages which will become clear from the description that
follows.
In accordance with a second aspect the invention provides a method
of making an electrofusion sleeve coupling comprising the steps of
preparing a cylindrical shell, winding a coil of electrical
resistance heating wire coated with thermoplastic material onto a
mould core, inserting the core and winding thereon into the shell
with a radial space defined therebetween, injecting thermoplastic
material to fill said space, and removing the core so that the
winding is retained in the shell by the moulded material.
The preparation of the shell preferably comprises machining the
shell and thereby forming an axially outwardly directed shoulder
adjacent each end thereof so that the layer of material
subsequently moulded in situ inside the shell abuts against the
shoulder for the purpose which has been explained above.
Conveniently, after inserting the core into the shell, a contact
part can be attached to the wire end and introduced into a radial
hole provided in the shell so that the contact part will be secured
in place by the moulded material. During the moulding step the
contact part can be secured in position by a fixing device engaged
with the contact part from outside the shell. With the connections
between the contact parts and wire ends embedded in the moulded
material they are protected and do not form protrusions against
which the pipe ends may snag when they are inserted into the
coupler.
The wire is preferably wound in two tightly wound sections in each
of which the adjacent turns contact each other, with a link portion
interconnecting these two sections.
The present invention is aimed mainly at the manufacture of large
diameter electro-fusion fittings, but there is no reason why it
should not be applied also to the production of smaller diameter
fittings if desired.
Most conveniently the shell is prepared from a tubular blank, e.g.
sawn off from an extruded thermoplastic pipe, or fabricated from an
extruded ribbon as described in more detail hereinafter. The blank
material is preferably the same as the injection moulded material,
but this is not essential. The inner surface of the blank is
machined to a uniform diameter but is left with a rough surface
finish to provide a key to improve the adhesion of the moulded
layer to the shell.
In accordance with a further aspect of the invention there is
provided a mould core for use in manufacturing an electro-fusion
sleeve, comprising two circular core parts, means for securing the
core parts together to define an axially continuous cylindrical
surface for receiving a winding of electric resistance heating
wire, an inlet for molten plastics plastic material in an outer end
face of one core part, and an outlet for the molten material
defined on the cylindrical surface at the interface between the
core parts.
In a preferred core construction the inlet extends axially through
the one core part and communicates with a plurality of radial
runners defined between the two core parts and opening at
respective outlets spaced apart around the cylindrical surface.
The outer surfaces of the core parts may be provided with means,
e.g., circumferential rims or projections for holding the winding
in place before and during the injection moulding process.
A clear understanding of the invention in its various aspects will
be had from the following more detailed description given with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is an axial cross-section through an electro-fusion sleeve
fitting embodying the present invention;
FIG. 2 is an enlarged detail showing that part of the fitting
circled in FIG. 1;
FIG. 3 is an end view of the fitting shown in FIG. 1;
FIG. 4 is a schematic longitudinal cross-section showing an
apparatus for preparing a shell blank for manufacturing the fitting
of FIG. 1;
FIG. 5 is a top plan of the apparatus shown in FIG. 4;
FIG. 6 is a side elevation, shown partially in section taken along
the line VI--VI in FIG. 7, of a mould core for use in manufacturing
the fitting shown in FIG. 1;
FIG. 7 is a right hand end elevation of the core shown in FIG.
6;
FIG. 8 is a section through the core taken along the line VII--VII
in FIG. 6; and
FIG. 9 is a transverse section illustrating an electrical contact
assembly prepared ready for the injection moulding step.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring initially to FIGS. 1 to 3, there is illustrated a pipe
coupler in the form of an electro-fusion sleeve fitting. The body
of the fitting consists mainly of a cylindrical shell or carcase 1
on the interior of which is arranged an electrical resistance wire
winding 2 held in place by an intervening layer 3 of injection
moulded thermoplastic material. The layer 3 extends from end-to-end
of the shell and at its ends is formed with chamfered faces 4
defining a lead-in for each pipe end to facilitate insertion of the
pipe ends to be joined into the sleeve. At the medial plane the
layer 3 defines a plurality of circumferential spaced studs which
project inwardly and define stops 5 for the pipe ends to abut
against, thereby to ensure correct positioning within the sleeve in
preparation for the welding process. At a small distance from each
end an annular groove 6 of rectangular cross-section is machined in
the shell 1 and the material of the layer 3 fills this groove to
provide a mechanical interlock between the shell and moulded layer.
This interlock prevents the layer 3 from breaking away from the
shell as a consequence of the radial and axial shrinkage effects
which occur in the layer 3 while it is cooling as part of the
injection moulding process.
The wire winding is wound in two coil sections which are contiguous
due to an integral wire section linking them and depicted
schematically in broken line in FIG. 1. The coil sections are
arranged for cooperation with respective pipe ends in well known
manner. The winding is formed from wire coated in thermoplastic
material which is preferably the same material as that of the layer
3 and ideally also the same as the material of the shell 1. In each
of the two coil sections the turns of the winding are arranged in a
single layer and in abutment with each other. By virtue of being
injection moulded in situ the layer 3 adheres strongly to the shell
and the coating of the wire winding, but it is not united
therewith, that is, until the welding process when the heat
generated in the winding by the electric current passed through it
causes the thermoplastic material at the boundary faces to melt and
fuse together, at least in the regions of the two coil sections,
whereby a strong fusion bond is obtained between the outer surface
of the pipe end in the sleeve, and the material of the wire
coating, layer 3 and the shell 1.
The ends of the wire are connected to contact pin assemblies for
connecting the winding to a source of electrical energy during the
welding process. As may be best seen in FIG. 2, an eye connector 8
is attached to the wire end by crimping and an inner contact part 9
having an enlarged inner end extends through the eye and into a
radial hole provided in the shell 1. The inner end of contact part
9 and the connector 8 are embedded in the layer 3 so that they do
not form any obstruction to and will not be damaged by a pipe end
being introduced into the welding sleeve. At its outer end the
contact part 9 has a threaded connection, in particular a tapped
core into which an outer contact part 10 is screwed. The contact
part 10 comprises a pin onto which a plastic shroud 11 is fitted or
moulded to surround an outer pin contact end, and the inner end of
the pin is screw threaded for engagement with the inner contact
part, as shown. During the pipe welding process the two pin
contacts of the fitting are connected to an electric current source
in well known manner.
Because the space between the shell 1 and the electrical winding 2
is filled by the layer 3, it is not necessary for the shell to be
manufactured to close tolerances or to be expanded and/or shrunk
while applying the winding into the shell. The shell could be
prepared from a tubular blank cut from an extruded plastics pipe,
but an alternative method of making a tubular blank is shown in
FIGS. 4 and 5. A conventional plastics extruder 12 and an extrusion
die 13 are used to produce a flat ribbon extrudate 15 of
essentially rectangular section. The extrudate is led to a winding
drum 14 and is wound onto the drum until the desired thickness has
been built up. A pressure roller 16 is used to press the extrudate
onto the underlying layers already on the drum to ensure close
intimate contact. The cylindrical shell blank thus produced may be
subject to annealing and is then machined ready for producing an
electro-fusion fitting. The blank is machined over its inner and
outer surfaces, including the machining of the grooves 6, and is
drilled with the radial holes to accept the contact terminal
assemblies. As already mentioned above, the shell can be made to
large tolerances and the machining needs only to give the
approximate dimensions. It is actually best for the inside surface
to be machined to a relatively rough finish, e.g. to provide a
helical ridge which increases the surface area, to improve the
adhesion of the injection moulded layer to this surface.
In the injection moulding step, i.e., during the formation of the
layer 3, the shell 1 constitutes an outer mould part delimiting the
mould cavity with a mould core. The core is shown in FIGS. 6 to 8,
but it should be noted that FIG. 6 is not a true section insofar as
some parts, mainly bolt 24 and dowels 35, are shown out of true
position for ease of illustration. The core has an outer
cylindrical surface with circumferential end rims 20 for producing
the chamfer faces 4 as described above. Spaced a short distance in
from the rims are further circumferential projections 21 which
define axially inwardly directed radial stop shoulders which serve
to locate the outer ends of the respective heating coil sections
and to hold them in position during injection of the moulding
material. The core is made in two axial halves 22, 23 which are
held together by a detachable bolt 24. To ensure correct coaxial
alignment between the core halves, the core half 23 is equipped
with two diametrically opposed location dowels 25 which enter
corresponding bores 26 in the core half 22 when the two halves are
brought together. The core half 22 is equipped with an axial sprue
bush 27 defining an inlet channel 28 for the moulding material, the
inner end of the channel opening into six radial runners 30
uniformly distributed around the axis and having gates 31 opening
at the cylindrical surface of the core. The runners are confined
between the confronting faces of the core halves and have their
gates shaped for producing the stops 5 mentioned above.
Accommodated in recesses in the outer end faces of the core halves
are extraction plates 32 fixed in position by bolts 33. In each
plate 32 there are three key-hole shaped slots 34 which are
undercut behind their narrow portions enabling enlarged heads of an
extraction tool to be inserted and by a small angular rotation be
securely locked to the extraction plate and hence the core half.
With extraction tools so engaged with the two core halves they can
be pulled apart and in opposite directions out from a completed
electrofusion fitting, the bolt 24 having been removed first of
course. It will be noted that the head of bolt 24 is located in a
slot 35 in the extraction plate of core half 22. The corresponding
extraction tool has a projection arranged to enter this slot and if
the bolt 24 has not been removed the extraction tool cannot be
engaged with the extraction plate. For support and correct
positioning of the core within the injection moulding machine, the
extraction plates are provided with tapered location recesses 36.
It will be noted that the sprue bush is fixed in the core half 22
by its extraction plate 32.
The core halves are formed with removable core segments 38. When
the core is inserted into the shell these segments, or at least the
spaces they normally occupy, are positioned opposite the holes
provided in the shell to receive the contact terminal assemblies,
for reasons which are explained below.
With the core assembled as shown in the drawings, the coated
electrical resistance wire is wound onto the core to form the two
coil sections, respectively abutting with their outer ends the stop
faces of rims 21, with the wire ends being left protruding at the
position of the removable core segments 38. The core and winding
are inserted axially into the previously prepared shell. The
segments 38 are removed so that the eye connectors 8 can be crimped
onto the wire ends, and the inner contact parts 9 are inserted
through the eyes and into the holes in the shell. To secure them
firmly during the injection moulding process, a mould tool bung 39
(FIG. 9) generally formed as a bolt is screwed into each contact
part 9 and serves to clamp it firmly against the interior surface
of the shell. The segments are then replaced and the entire
assembly of shell and core is loaded into a suitable injection
moulding machine. The thermoplastics material is injected through
the sprue bush and enters the cavity confined between the shell 1
and core via the runners 30 and gates 31 to fill this space and
thereby form the layer 3 for holding the winding on the interior
surface of the shell. After an appropriate curing time, the
assembly is removed from the moulding machine and the core halves
22, 23 can be removed by extraction tools engaged with the core
halves as explained above. All that remains to complete the fitting
is to remove the mould tool bungs 39 and insert in their place the
outer contact parts 10. If preferred, to remove any risk of damage
during storage and/or transportation, the outer contact parts may
be fitted only when the electro-fusion is ready to be used to
produce a welded pipe joint. It will be noted that apart from being
convenient from a manufacturing viewpoint the two-part contact
assembly has the advantage that different outer contact parts could
be applied, e.g., to suit the particular contact configurations of
different control devices which may be used to supply electric
power to the fitting.
It will be understood that modifications are possible without
departing from the scope of the invention. Hereby as an example it
is mentioned that other forms of connector may be used to connect
the wire ends to the contacts, rather than the eye connectors shown
and described, or if the contacts are suitably made a direct
connection with the wire is possible. Thus the wire end could be
inserted into a transverse bore provided in the inner end of
contact part 9 and be securely clamped therein by a grub screw
screwed into the tapped core of part 9 ahead of the outer contact
part 10.
* * * * *